This invention is in the field of digital communications, and is more specifically directed to the establishing and termination of service flows in wireless communications.
Advances in wireless communication technology, especially in recent years, have greatly improved not only the performance (i.e., data rate for a given error rate) at which wireless communications can be carried out, but have also enabled the realization of additional functions and services by way of wireless communications. For example, wireless broadband communications in metro area networks is now becoming commonplace. An example of one type of wider area wireless network communications is referred to as “WiMAX”, corresponding to communications carried out under IEEE Standard for Local and metropolitan area networks, Part 16: Air Interface for Fixed Broadband Wireless Access Systems (IEEE Standard 802.16-2004, and all subsequent revisions). Of course, wireless local area networks (WLAN) are now also becoming commonplace, and are capable of carrying traffic at very high data rates (e.g., 1 Gbit/sec).
Networks operating under the WiMAX standard, for example, are capable of carrying out multiple types of communications. These multiple communications “services” are typically supported by modern wireless devices, including laptop computers equipped with WiMAX network adapters, palm top computers or highly capable personal digital assistants (PDAs), and modern “smartphones” that support data services. As known in the art, these modern wireless devices and systems, communicating via a WiMAX or other metro or wider area wireless network, support multiple simultaneous wireless communications sessions. Different types of such communications can have different constraints and requirements. For example, one class of such communications that can be carried out under WiMAX is voice telephony, for example by way of the well-known Voice over Internet Protocol (VoIP) service. VoIP communications involve constraints on the timeliness of the communications (i.e., so that a sensible back-and-forth conversation can be carried out), but can tolerate a relatively high error rate. In contrast, email services, and web browsing services over the Internet, involve less stringent time constraints, but can have higher error rate requirements.
Physically, a WiMAX metro area network is realized via base stations deployed within the physical service area with some frequency (e.g., on the order of a base station deployed every mile, to every several miles), similar to cellular telephone base stations and towers. A given base station is capable of communicating with nearby wireless client devices, typically referred to as “subscriber stations”, or often as “mobile stations” considering that these devices are typically portable computing and communications devices such as laptop or palmtop computers, smartphones, and the like. Each of the traffic flows between a mobile station and a base station is typically referred to as a “service flow”, in the context of WiMAX communications. For example, a VoIP call is carried out over one service flow, an email session is carried out over another service flow, and each web browsing session is carried out over another service flow. As evident from this discussion, multiple service flows may be carried out simultaneously between a mobile station and a base station; indeed, communications in each direction (e.g., uplink and downlink) is typically considered a separate service flow, such that bidirectional communications in an interactive web session, for example, typically constitutes two service flows.
Under conventional communications under the IEEE 802.16 standard, a service flow is established at the request of either the base station or the mobile station, regardless of whether the requesting station is to transmit or receive the payload traffic. FIG. 1a illustrates the operation of establishing a service flow in such conventional wireless broadband communications. As shown in FIG. 1a, the requesting station (“initiator”) transmits a request (referred to as a Dynamic Service Addition Request, or DSA-REQ, under IEEE 802.16) to establish the service flow to the other station (“responder”). The request can include data rate requirements and other parameters, and can also specify bidirectional communications by way of a flag setting in that request. The responder in turn transmits a response (Dynamic Service Addition Response, or DSA-RSP) to the initiator, indicating whether the responder can comply with the request, and possibly including proposed changes to the data rate requirements and other parameters as may be necessitated or desired by that station. The initiator then issues an acknowledgement (Dynamic Service Addition Acknowledgement, or DSA-ACK) to the responder, accepting the service flow as modified by the responder, or denying the modification and thereby aborting the service flow. If the acknowledgement accepts the service flow, as in the situation shown in FIG. 1a, traffic can then flow between the mobile station and base station, in the direction indicated in the original request (download or upload), or bidirectionally if the request so indicated.
However, under conventional 802.16 communications, an ambiguity can arise if a valid acknowledgement (DSA-ACK) sent by the initiator is not received by the responder. This situation is illustrated in FIG. 1b. Under the standard, if the responder does not receive the acknowledgement within a certain time-out period, it will retransmit the response (DSA-RSP) and again wait for the acknowledgement. If the error condition persists (either because the initiator does not receive the response message, or if the acknowledgement by the initiator is not received by the responder), the responder will continue issuing the response (DSA-RSP “retry” as shown in FIG. 1b) for a specified number of times, following which the responder will assume that the service flow is not established. Under the 802.16 standard, however, if the initiator is receiving each of these response messages as valid, and is issuing the acknowledgement in return, after its transmission of the last acknowledgement (DSA-ACK), it will assume that the responder has validly received this acknowledgement, and that the service flow is established. If the initiator of the service flow is the intended receiver of the payload, this situation is not particularly detrimental, because the unaware transmitting responder will not begin transmission of the payload traffic without receiving a valid acknowledgement from the initiator. Eventually, in this situation, the initiator may delete the service flow after elapse of a timeout period during which it receives no payload traffic. But in the unfortunate event that the initiator is also the intended transmitter of payload under the service flow, as in the example of FIG. 1b, this transmitting initiator station will transmit payload traffic unconditionally, following its issuance of the acknowledgement. This initiator will have resources assigned to transmit payload data, and will transmit that payload data, but the receiver will be ignoring or not receiving the transmission. This condition uselessly consumes resources of the transmitter station, and if the transmitter is a mobile station, will likely be uselessly consuming battery power.
By way of further background, under the IEEE 802.16 standard, a message requesting deletion of a service flow (Dynamic Service Deletion Request, DSD-REQ), may be transmitted by either the base station or the mobile station, in response to which the particular service flow is terminated, following a response from the other station (Dynamic Service Deletion Response, DSD-RSP).